Lava Extrusion Research Articles

Effects of cohesion and viscosity on lava dome growth following repose

Lava domes result from effusive eruption of high viscosity lava. These viscous lava extrusions range in shape from flat-topped domes with small height-to-width aspect ratios, to spine-like columns exhibiting large height-to-width aspect ratios. A primary control on morphology during early dome growth is thought to be the variation in rheological characteristics of extruded material. In this work, we present new scaled analogue models of lava dome growth that consider extrusion of a frictional plastic upper-conduit plug followed by viscous magma. We simulate the brittle plug using a sand-plaster mixture, the cohesion of which is varied by plaster content. We model the magma using sugar syrup, the viscosity of which is controlled by the weight percent of added crystalline sugar. The models both qualitatively and quantitatively reproduce part of the spectrum of natural dome morphology not previously obtained in most past analogue modelling studies. Model aspect ratios of 0.02 to 0.9 capture approximately 90 % of the reported aspect ratio variation in nature. Increasing plug cohesion results in extrusions with higher aspect ratios and spinier morphologies. Low viscosity fluid typically erupts through the brittle dome, whilst high viscosity fluid tends to promote endogenous growth or emerge as exogenous lobes. Particle Image Velocimetry shows that fracture localisation at the dome surface is cohesion-dependent, and eruption of fluid follows shear fractures within the dome. Where fluid remains contained within the dome, we see lateral spread leading to a wider and flatter dome morphology. Evolution of lava dome morphology, deformation, and associated hazards is guided by the complex rheological properties of the extruded material; we suggest that during episodic dome growth, these properties are largely defined in the conduit prior to their eruption.

Time scales and mechanisms of uranium uptake in altered ocean crust; observations from the ∼15 million year-old site 1256 in the eastern equatorial Pacific

The alteration of ocean crust through hydrothermal seawater circulation facilitates chemical exchange between Earth’s surface and interior. Hydrothermal alteration leads to uranium (U) removal from seawater and net U uptake by the ocean crust, particularly during low temperature alteration that occurs on the vast ocean ridge flanks away from the spreading axes. Determining the timescales of U uptake and its associated 238U/235U signature has important implications for understanding U exchange processes during subduction and recycling into the mantle. Here we study the U systematics of ∼15 million year-old ocean crust drilled at Site 1256 on the eastern flank of the East Pacific Rise. Analysis of cores from the upper ∼1300 m of intact ocean crust at this site, reveal large variability in U concentrations and 238U/235U ratios. Many of the samples from the upper ∼600 m of extrusive lavas have elevated U concentrations and 238U/235U ratios lower than seawater, consistent with mechanisms of U uptake under relatively oxidised conditions. Samples from the underlying sheeted dikes and gabbros show evidence for hydrothermal U mobilisation, but negligible net U uptake. In contrast, in the transition zone between the extrusive lavas and the sheeted dikes, samples revealed large U enrichments and high 238U/235U ratios above seawater. This is consistent with uptake of the reduced U+4 species under relatively reducing conditions from seawater-derived hydrothermal fluids. In addition, large secular disequilibrium in 234U/238U ratios from samples in the lava-dike transition and upper sheeted dikes give evidence for U mobility within the last ∼1.5 million years, likely driven by deep channelled flow of seawater-derived hydrothermal fluids combined with preferential leaching of 234U from the rock matrix. Both the total estimated U uptake and mean 238U/235U at Site 1256 is lower than similar estimates from significantly older (>100 million years) altered ocean crusts at drill Sites 801 and 417/418. This shows the variable total U uptake and 238U/235U ratio in altered ocean crust over time, which needs to be taken into consideration when estimating global U budgets.

Emplacement of shergottites in the Martian crust inferred from three‐dimensional petrofabric and crystal size distribution analyses

AbstractShergottites are mafic to ultramafic igneous rocks that represent the majority of known Martian meteorites. They are subdivided into gabbroic, poikilitic, basaltic, and olivine–phyric categories based on differences in mineralogy and textures. Their geologic contexts are unknown, so analyses of crystal sizes and preferred orientations have commonly been used to infer where shergottites solidified. Such environments range from subsurface cumulates to shallow intrusives to extrusive lava flows, which all have contrasting implications for interactions with crustal material, cooling histories, and potential in situ exposure at the surface. In this study, we present a novel three‐dimensional (3‐D) approach to better understand the solidification environments of these samples and improve our knowledge of shergottites' geologic contexts. Shape preferred orientations of most phases and crystal size distributions of late‐forming minerals were measured in 3‐D using X‐ray computed tomography (CT) on eight shergottites representing the gabbroic, poikilitic, basaltic, and olivine–phyric categories. Our analyses show that highly anisotropic, rod‐like pyroxene crystals are strongly foliated in the gabbroic samples but have a weaker foliation and a mild lineation in the basaltic sample, indicating a directional flow component in the latter. Star volume distribution analyses revealed that most phases (maskelynite, pyroxene, olivine, and oxides/sulfides) preserve a foliated texture with variable strengths, and that the phases within individual samples are strongly to moderately aligned with respect to one another. In combination with relative cooling rates during the final stages of crystallization determined from interstitial oxide/sulfide crystal size distribution analyses, these results indicate that the olivine–phyric samples were emplaced as shallow intrusives (e.g., dikes/sills) and that the gabbroic, poikilitic, and basaltic samples were emplaced in deeper subsurface environments.

Tremor clustering reveals pre-eruptive signals and evolution of the 2021 Geldingadalir eruption of the Fagradalsfjall Fires, Iceland

Analyzing seismic data in a timely manner is essential for potential eruption forecasting and early warning in volcanology. Here, we demonstrate that unsupervised machine learning methods can automatically uncover hidden details from the continuous seismic signals recorded during Iceland’s 2021 Geldingadalir eruption. By pinpointing the eruption’s primary phases, including periods of unrest, ongoing lava extrusion, and varying lava fountaining intensities, we can effectively chart its temporal progress. We detect a volcanic tremor sequence three days before the eruption, which may signify impending eruptive activities. Moreover, the discerned seismicity patterns and their temporal changes offer insights into the shift from vigorous outflows to lava fountaining. Based on the extracted patterns of seismicity and their temporal variations we propose an explanation for this transition. We hypothesize that the emergence of episodic tremors in the seismic data in early May could be related to an increase in the discharge rate in late April.

A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Hawaiian Ridge: 1

AbstractThe Hawaiian Ridge has long been a focus site for studying lithospheric flexure due to intraplate volcano loading, but crucial load and flexure details remain unclear. We address this problem using wide‐angle seismic refraction and reflection data acquired along a ∼535‐km‐long profile that intersects the ridge between the islands of Maui and Hawai'i and crosses 80–95 Myr‐old lithosphere. A tomographic image constructed using travel time data of several seismic phases reveals broad flexure of Pacific oceanic crust extending up to ∼200–250 km either side of the Hawaiian Ridge, and vertically up to ∼6–7 km. The P‐wave velocity structure, verified by gravity modeling, reveals that the west flank of Hawaii is comprised of extrusive lavas overlain by volcanoclastic sediments and a carbonate platform. In contrast, the Hāna Ridge, southeast of Maui, contains a high‐velocity core consistent with mafic or ultramafic intrusive rocks. Magmatic underplating along the seismic line is not evident. Reflectors at the top and bottom of the pre‐existing oceanic crust suggest a ∼4.5–6 km crustal thickness. Simple three‐dimensional flexure modeling with an elastic plate thickness, Te, of 26.7 km shows that the depths to the reflectors beneath the western flank of Hawai'i can be explained by volcano loading in which Maui and the older islands in the ridge contribute ∼43% to the flexure and the island of Hawai'i ∼51%. Previous studies, however, revealed a higher Te beneath the eastern flank of Hawai'i suggesting that isostatic compensation may not yet be complete at the youngest end of the ridge.

Numerical thermomechanical modelling of lava dome growth during the 2007–2009 dome-building eruption at Volcán de Colima

SUMMARY Lava domes form during effusive eruptions due to an extrusion of highly viscous magmas from volcanic vents. In this paper we present a numerical study of the lava dome growth at Volcán de Colima, Mexico during 2007–2009. The mathematical model treats the lava dome extrusion dynamics as a thermomechanical problem. The equations of motion, continuity and heat transfer are solved with the relevant boundary and initial conditions in the assumption that magma viscosity depends on the volume fraction of crystals and temperature. We perform several sets of numerical experiments to analyse the internal structure of the lava dome (i.e. the distributions of the temperature, crystal content, viscosity and velocity) depending on various heat sources and thermal boundary conditions. Although the lava dome growth at Volcán de Colima during short (a few months) dome-building episodes can be explained by an isothermal model of lava extrusion with the viscosity depending on the volume fraction of crystals, we show here that cooling plays a significant role during long (up to several years) episodes of dome building. A carapace develops as a response to a convective cooling at the lava dome–air interface. The carapace becomes thicker if the radiative heat loss at the interface is also considered. The thick carapace influences the lava dome dynamics preventing its lateral advancement. The release of the latent heat of crystallization leads to an increase of the temperatures in the lava dome interior and to a relative flattening of the dome. Meanwhile, the heat source due to viscous dissipation inside the lava dome is negligible, and it does not influence the lava dome growth. The developed thermomechanical model of the lava dome dynamics at Volcán de Colima can be used elsewhere to analyse effusive eruptions, dome morphology and carapace evolution including its failure potentially leading to pyroclastic flow hazards.

Cooling history (from magma ascent to lava extrusion) of the Watuadeg pillow lava, Berbah, Yogyakarta, Indonesia

The Watuadeg pillow lava (WPL) is known as one of the most famous pillow lava outcrops in Yogyakarta, Indonesia, and its origin has been attributed to rapid-cooling process of subaqueous lava extrusion. However, there is no quantitative evidence that implies such hypotheses. Therefore, this study aims to reduce such a gap by revealing the cooling times (t) of WPL on the basis of a quantitative approach. In particular, we measured the size distribution (CSD) and number density (MND) of plagioclase microlites from the core, medial, and marginal (rim) domains of WPL. We found that the CSD slope significantly increases towards marginal zones, namely 30.4ᵒ for the core, 53.4ᵒ for the medial, and 228.1ᵒ for the rim. Because CSD slope is inversely proportional to cooling time ( ), by assuming a typical plagioclase microlite growth rate (G) of 1×107 mm/s, it is therefore inferred that the rim experienced the fastest cooling time (±12.1 hours), followed by the medial and core ((±52.0 and 91.4 hours, respectively). The fact that MNDs value increases toward the marginal zones also does not deny this idea (0.3×1016 m-3 for the core, 1.4×1016 m-3 for the medial, and 2.4×1016 m-3 for the rim), as higher MND with the domination of acicular-spherulitic habit represents a higher degree of undercooling. Because microlite is syn-eruptive product, our estimation represents the cooling time of magma since it migrated from the reservoir to the surface.

Lava – substrate interaction: Constraints on flow emplacement and basal sintering, Lebuj rhyolitic flow, Tokaj Mountains, Carpathian-Pannonian region

The surface extrusion of rhyolite lava is linked with a complex edifice morphology and texturally diverse internal structure. The rarely exposed basal flow/dome zones provide a textural record of the mechanical and thermal stress between the overlying lava and existing topography. The Lebuj flow (Tokaj Mountains, Hungary) developed in a Miocene caldera setting, where the erosion exposed its basal zone, including various textures due to the lava substrate interaction. The flow margin is contacted with underlying volcaniclastics along a steeply inclined (50–75°) plane. The lithology describes a complex ductile-brittle transition in the flow and lithification process in the substrate. The relict obsidian grains (marekanite, 0.1% H2O) in the perlite (2–3% H2O) are proof of an incomplete hydration process below the glass transition temperature. The dynamic loading of the lava caused irregular fragmentation developing a brittle basal shear zone with lens-like glass deformation. The substrate has suffered syn-emplacement lithification and the primary glass structure is completely re-crystallized. FTIR and Raman measurements identified low-temperature phyllosilicate minerals and SiO2 polymorphs, which caused additional porosity loss and densification. Using cooling time-temperature-porosity information given by this reconstruction, we suggest parallel-acting processes at elevated (groundmass crystallization-devitrification) and lower temperature (hydration-secondary mineralization) range. These define a relative timescale for the textural development in the lithologically heterogeneous contact zone.

Temporal Variability in Gas Emissions at Bagana Volcano Revealed by Aerial, Ground, and Satellite Observations

AbstractBagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano's summit plume, and a payload comprising a miniaturized MultiGAS. We combine our measurements of the molar CO2/SO2 ratio in the plume with coincident remote sensing measurements (ground‐ and satellite‐based) of SO2 emission rate to compute the first estimate of CO2 flux at Bagana. We report low SO2 and CO2 fluxes at Bagana from our fieldwork in September 2019, ∼320 ± 76 td−1 and ∼320 ± 84 td−1, respectively, which we attribute to the volcano's low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana's activity and emissions behavior are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS‐type instruments for remote monitoring of gas emissions from other inaccessible volcanoes.

Строение, петрография и петрогеохимия кислых пород экструзивно-субвулканического тела южной части хребта Енганепэ (Полярный Урал)

The results of the study of textural and structural features of acidic volcanites of the extrusive-subvolcanic body of the Lyadgey Complex (V2ld) between the Pravy Izyavozh and the Levy Izyavozh creeks of the southern part of the Enganepe Ridge are reported. We found that the extrusive-subvolcanic formation had an inhomogeneous structure due to the zonal arrangement of rock varieties: massive, fluid and spheruloid rhyolites, clusters of rhyolite and dacite composition. Prominence in relief, signs of extrusion of viscous lava, flow textures, successive change from west to east of fluid varieties by massive and then spheroid, the presence of clastolaves of rhyolite and dacitic compositions allow classifying the studied object as an extrusive genetic type.

A New Model for the Evolution of Oceanic Transform Faults Based on 3D Broadband Seismic Observations From São Tomé and Príncipe in the Eastern Gulf of Guinea

AbstractOceanic Transform Faults are one of manifestations of the three major plate boundaries and a key tectonic feature of oceanic crust. They are broadly considered to accommodate strike‐slip displacement along simple vertical faults and to be largely without magmatic addition. We present the first observations from broadband 3D seismic of buried, Cretaceous‐aged transform faults in the Gulf of Guinea with complex internal architectures including crustal scale detachments and rotated packages of volcanics within oceanic crust. In the study area, several Oceanic Fracture Zones (OFZ) are described from Top Crust to Moho. OFZ scarps are observed to connect at depth with zones of low angle reflectivity which dip into the OFZ and perpendicular to the spreading orientation. At depth they detach onto the Moho, necking the adjacent crust in the manner of extensional shear zones. Thickly stacked and tilted reflectors, interpreted as extrusive lava flows, are common above the shear zones and infill up to 75% of the crustal thickness. The entire OFZ stratigraphy is overlain and sealed by late‐stage lavas that are continuous from the abyssal hills of the trailing spreading ridge. These insights demonstrate complexity previously only predicted in numerical simulations. We propose a model with extension at a high angle to the spreading orientation along a low angle shear zone that acts as a conduit for decompression related melt and volcanism. We conclude that oceanic transforms are non‐conservative and not simple strike slip fault zones, contradicting the conventional view.

Large-scale lava dome fracturing as a result of concealed weakened zones

Abstract Mechanically weakened alteration zones in lava domes are thought to jeopardize their stability. Such zones can be hazardous when concealed within the dome, either because they formed by subsurface hydrothermal circulation or because they formed on the surface but were subsequently buried by renewed lava extrusion. We present a new suite of computational models showing how the size and position of a weakened brittle zone within a dome can affect large-scale fracture formation, displacement, and the collapse mechanism. By combining recent laboratory data for the mechanical behavior of dome rocks with discrete element method models, we show (1) the presence of a weak zone increases instability, which is exacerbated when the size of the zone increases or the zone is positioned off-center; (2) the position of the weak zone changes the deformation mechanism from slumping-type slope deformation when the zone is positioned centrally, compared with deep-seated rotational slope failure when the zone is positioned toward the dome flank; and finally, (3) dome-cutting tensile fractures form in the presence of a small weak zone (60 m diameter, ∼14% of dome width), whereas large weak zones (120 m diameter, ∼27% of dome width) promote the formation of longer and deeper fractures that jeopardize larger dome volumes. Our results corroborate previous field observations at lava domes and indicate that large fracture formation, which greatly influences dome stability and outgassing, can be explained by the presence of concealed alteration zones. This improved understanding of the mechanisms responsible for dome instability enables better hazard assessment at volcanoes worldwide.

Outgassing through magmatic fractures enables effusive eruption of silicic magma

Several mechanisms have been proposed to allow highly viscous silicic magma to outgas efficiently enough to erupt effusively. There is increasing evidence that challenges the classic foam-collapse model in which gas escapes through permeable bubble networks, and instead suggests that magmatic fracturing and/or accompanying localized fragmentation and welding within the conduit play an important role in outgassing. The 2011–2012 eruption at Cordón Caulle volcano, Chile, provides direct observations of the role of magmatic fractures. This eruption exhibited a months-long hybrid phase, in which rhyolitic lava extrusion was accompanied by vigorous gas-and-tephra venting through fractures in the lava dome surface. Some of these fractures were preserved as tuffisites (tephra-filled veins) in erupted lava and bombs. We integrate constraints from petrologic analyses of erupted products and video analyses of gas-and-tephra venting to construct a model for magma ascent in a conduit. The one-dimensional, two-phase, steady-state model considers outgassing through deforming permeable bubble networks, magmatic fractures, and adjacent wall rock. Simulations for a range of plausible magma ascent conditions indicate that the eruption of low-porosity lava observed at Cordón Caulle volcano occurs because of significant gas flux through fracture networks in the upper conduit. This modeling emphasizes the important role that outgassing through magmatic fractures plays in sustaining effusive or hybrid eruptions of silicic magma and in facilitating explosive-effusive transitions.

Probabilistic analysis to correlate seismic data with lava extrusion phases at Merapi volcano (Indonesia)

Volcanoes can produce a range of eruptive behavior even during a single eruption, changing quickly from effusive to explosive style, and the other way around. The changes in eruption phases (e.g. phreatic explosion, magmatic explosion, lava extrusion, etc.) can lead to different volcanic hazards and require timely assessment for the implementation of mitigation measures. Here we explore how to correlate a given eruption phase with changes in the monitoring data using statistical analysis and conditional probabilities. We calculate the success of detection of an eruption phase using a threshold of monitoring data, which includes the uncertainty on the eruption phase dates with a Monte Carlo simulation. We apply the method to dome forming eruptions of Mt. Merapi (Indonesia) and evaluate their time occurrence using an exceptionally long monitoring time series (from 1993 to 2012, over nineteen years) of Multiphase (Hybrid) Seismic Energy. We identify the seismic energy threshold that is associated with the lava extrusion phase with an accuracy of 90 ±2%, precision of 73 ± 2%, specificity of 96 ± 1%, and sensitivity of 56 ± 1%. We further test our method with the recent 2018 eruption (not used in the thresholds calculations) and we identify the lava extrusion with a precision of 67%, specificity of 70%, and sensitivity of 92%. We also seismically detected the 2018′s onset of the lava extrusion phase 14 days earlier than the visual observation. Given the link between dome-collapse pyroclastic flows and growth episodes of the lava dome at Merapi, our analysis also allows us to establish that 83% of the most energetic pyroclastic flows occur within the first 3 months after the onset of lava extrusion phase. Our method can be applicable to a range of time series of monitoring data (seismic, deformation, gas) and to other volcanoes that have a significant number of past events.

Hidden mechanical weaknesses within lava domes provided by buried high-porosity hydrothermal alteration zones

Catastrophic lava dome collapse is considered an unpredictable volcanic hazard because the physical properties, stress conditions, and internal structure of lava domes are not well understood and can change rapidly through time. To explain the locations of dome instabilities at Merapi volcano, Indonesia, we combined geochemical and mineralogical analyses, rock physical property measurements, drone-based photogrammetry, and geoinformatics. We show that a horseshoe-shaped alteration zone that formed in 2014 was subsequently buried by renewed lava extrusion in 2018. Drone data, as well as geomechanical, mineralogical, and oxygen isotope data suggest that this zone is characterized by high-porosity hydrothermally altered materials that are mechanically weak. We additionally show that the new lava dome is currently collapsing along this now-hidden weak alteration zone, highlighting that a detailed understanding of dome architecture, made possible using the monitoring techniques employed here, is essential for assessing hazards associated with dome and edifice failure at volcanoes worldwide.

Integrated petrological and Fe-Zn isotopic modelling of plutonic differentiation

The upper continental crust is formed from chemically diverse granitic plutons. Active debate surrounds the range of physical conditions (P-T-X-fO2) and differentiation processes which occur in mush bodies that solidify to form plutons. Transition metal stable isotopes are increasingly employed to trace magmatic processes in both extrusive lavas and intrusive plutonic suites, with a focus on analysis of whole rock powders. However, studies of plutonic suites often overlook the complex textures represented within coarse grained samples, and how these will influence whole rock isotopic compositions.Here we examine the calc-alkaline Boggy Plain Zoned Pluton, SE Australia, which closely approximates closed system behaviour during magmatic differentiation. We combine petrological examination with Fe and Zn isotopic analysis of biotite, hornblende and magnetite mineral separates and whole rock powders. Whole rock Fe isotopic composition (as δ56Fe) increases from 0.038‰ to 0.171‰ with decreasing MgO content, while mineral separates display heavy Fe isotope enrichment in the order magnetite > biotite = hornblende > pyroxene. A lack of correlation between whole rock Fe and Zn isotopic compositions suggests that the Fe isotopic variation is predominantly driven by closed system fractional crystallisation: specifically by the balance between crystallisation of isotopically heavy magnetite, and isotopically light silicates. To demonstrate this quantitatively, temperature dependent mineral-melt fractionation factors were derived from the mineral separate data (Δ56Femag-melt = 0.17 × 106/T2 and Δ56Febt/hbd-melt = −0.12 × 106/T2) and used to construct models that successfully reproduce the observed Fe isotopic variation during fractional crystallisation. These fractionation factors are compared to theoretical and empirical estimates from previous studies. We highlight that accurate determinations of temperature and modal mineralogy are critical when modelling Fe isotopic variations in plutonic suites. Successful interpretation of equilibrium Fe isotopic fractionation in a relatively simple calc-alkaline suite like the Boggy Plain Zoned Pluton paves the way for Fe isotopes to be used to investigate more complex mush bodies.

Lava Dome Morphology and Viscosity Inferred From Data-Driven Numerical Modeling of Dome Growth at Volcán de Colima, Mexico During 2007-2009

Magma extrusion, lava dome growth, collapse of domes, and associated pyroclastic flow hazards are among important volcanological studies. In this paper, we analyze the influence of the magma viscosity and discharge rates on the lava dome morphology at Volcán de Colima in Mexico during a long dome-building episode lasting from early 2007 to fall 2009 without explosive dome destruction. Camera images of the lava dome growth together with recorded volumes of the erupted lava have been used to constrain numerical modeling and hence to match the history of the dome growth by nudging model forecasts to observations. Our viscosity model incorporates crystal growth kinetics and depends on the characteristic time of crystal content growth (or CCGT) and the crystal-free magma viscosity. Initially, we analyze how this viscosity, CCGT, and the rate of lava extrusion influence the morphology of the growing dome. Several model scenarios of lava dome growth are then considered depending on the crater geometry, the conduit location, the effective viscosity of dome carapace, and the extrusion rates. These rates are determined either empirically by optimizing the fit between the morphological shape of modeled domes and that of the observed dome or from the recorded lava dome volumes. The maximum height of the modeled lava dome and its horizontal extent are in a good agreement with observations in the case of the empirically-derived extrusion rates. It is shown that the topography of the crater at Volcán de Colima is likely to be inclined toward the west. The viscosity of the modeled lava dome (∼1012 Pa s) is in a good agreement with the effective viscosity estimated experimentally from lavas of Volcán de Colima. Due to the interplay between the lava extrusion and the gravity forces, the dome reaches a height threshold, and after that a horizontal gravity spreading starts to play an essential role in the lava dome evolution. The model forecasts that the dome carapace of higher viscosity (∼1014 Pa s) influences the dome growth and its morphology during long dome-building episodes by retarding horizontal advancement and developing steep-sided eastern edge of the dome at the volcano. The developed model can be used in assessments of future effusive eruptions and lava dome growth at Volcán de Colima or elsewhere. History matching modeling of lava dome growth sheds a light on dynamic processes inside the dome and may assist in assessing stress state in the dome carapace and in forecasting the dome failures.

Viscosity of evolving magmas: a case study of the Glass House Mountains, Australia

The viscosity of the remelted rock compositions of the Glass House Mountains, SE Queensland, Australia, has been determined via micro-penetration in the high-viscosity regime (108–1013 Pa s). The heat capacity of these melts has also been determined from room temperature to above the glass transition. The combination of these two data sets allows the fitting of the viscosity data by the Adam-Gibbs equation using the configurational heat capacity Cpconf(Tg12) and configurational entropy Sconf(Tg12). The resulting fit parameters allow the robust extrapolation of the viscosity data to higher temperature and viscosities of 10–4 Pa s. This data can now be used in the discussion of the emplacement of the magmas of the plugs, laccoliths, sills and dykes that form the Glass House Mountains complex and the plate motion and the plume responsible for the volcano plugs. The large increase in viscosity of the evolving magma and the resulting decrease in discharge rate of the volcanic vents suggest that very little magma appeared as extrusive lavas or pyroclastic material and that the Glass House Mountains are mainly remnants of intrusive bodies exposed by erosion.

Ina Lunar Irregular Mare Patch Mission Concepts: Distinguishing between Ancient and Modern Volcanism Models

Abstract The Ina irregular mare patch, an ∼2 × 3 km summit depression on an ancient ∼22 km diameter shield volcano, displays two very enigmatic units: (1) dozens of dark convex-upward mounds and (2) a very rough, optically immature floor unit with very sharp morphologic contacts between the two. Controversy surrounds the age interpretation of Ina; superposed impact crater size–frequency distributions (CSFDs) suggest an age of ∼33 Ma, consistent with the presence of sharp contacts between the units and indicating that mare volcanism continues to today. Models of the terminal stages of volcano summit pit crater activity suggest an age coincident with the building of the shield, ∼3.5 Ga; these models interpret the CSFD age and sharp contacts to be due to an extremely porous lava lake floor and extrusion and solidification of magmatic foams. We present robotic–human exploration mission concepts designed to resolve this critical issue for lunar thermal evolution.

Seismic Structure, Gravity Anomalies and Flexure Along the Emperor Seamount Chain

AbstractThe Hawaiian‐Emperor seamount chain in the Pacific Ocean has provided fundamental insights into hotspot generated intraplate volcanism and the long‐term strength of oceanic lithosphere. However, only a few seismic experiments to determine crustal and upper mantle structure have been carried out on the Hawaiian Ridge, and no deep imaging has ever been carried out along the Emperor seamounts. Here, we present the results of an active source seismic experiment using 29 Ocean‐Bottom Seismometers (OBS) carried out along a strike profile of the seamounts in the region of Jimmu and Suiko guyots. Joint reflection and refraction tomographic inversion of the OBS data show the upper crust is highly heterogeneous withPwave velocities <4–5 km s−1, which are attributed to extrusive lavas and clastics. In contrast, the lower crust is remarkably homogeneous with velocities of 6.5–7.2 km s−1, which we attribute to oceanic crust and mafic intrusions. Moho is identified by a strongPmParrival at offsets of 20–80 km, yielding depths of 13–16 km. The underlying mantle is generally homogeneous with velocities in the range 7.9–8.0 km s−1. The crust and mantle velocity structure has been verified by gravity modeling. While top of oceanic crust prior to volcano loading is not recognized as a seismic or gravity discontinuity, flexural modeling reveals a ∼5.0–5.5 km thick preexisting oceanic crust that is overlain by a ∼8 km thick volcanic edifice. Unlike at the Hawaiian Ridge, we find no evidence of magmatic underplating.